While various methods of fabricating pistons have been provided heretofore, the present invention can be considered an improvement on the method described in the printed German application No. DE-05 32 22 582 and my corresponding U.S. Pat. No. 4,532,686 issued Aug. 6, 1985, in which a blank is die-forged to produce a piston head with a cylindrical flange bent from a disc-shaped blank into the piston crown flange.
The piston body can be provided with bores forming eyes through which the pivot pin is inserted to couple the piston or connecting rod to this position.
In these earlier systems, the piston shaft is an independent element and generally is formed by casting and and machining, the piston crown and the shaft or body being united by a screwthread arrangement.
A piston of the aforedescribed type has been found to be suitable for heavy Diesel engines and like machines.
For high-speed internal-combustion engines, namely high compression engines and like modern gasoline engines for automotive vehicles, such pistons are seldom completely satisfactory.
For high-speed internal-combustion engines of the high compression and high fuel efficiency type, composite or assembled pistons are not satisfactory and generally one-piece pistons, preferably of steel in an increasing number of cases, are desired.
In the past, one-piece steel piston have been fabricated by casting a steel body and then machining the same to the desired dimensions and configuration.
Obviously, this method of fabrication is expensive but, even more important is the fact that this fabrication method does not provide a one-piece piston with optimum structural properties. For example, neither the strength nor distortion-resistance characteristics are satisfactory in many cases and especially where the structure is comparatively thin-walled, both strength and freedom from distortion may be lacking.